1. Field of the Invention
This invention relates to a process for delivering a selected effective amount of a dry granular antimicrobial composition to an aqueous system.
2. Brief Description of the Background Art
Aqueous water systems are susceptible to microbiological growth such as for example bacteria, yeast, fungi and algae. This microbiological growth presents a problem to many industrial and commercial applications, and more specifically includes, but is not limited to the fouling of the components of cooling water systems. Aqueous systems that become infected with microorganisms experience substantial impairment of their efficiency when deposits of the microorganisms build up in the system. These deposits coat the walls of heat exchangers and other vessels, machinery and other processing equipment employed, thus eventually creating blockages in and/or reducing heat transfer.
A variety of processes have been proposed to introduce a biocidal agent to an aqueous system for controlling this microbiological growth. It is generally well known by those skilled in the art to introduce a biocide into an aqueous system by manually dumping a quantity of a granular biocide, such as for example bromine or chlorine, to a vessel, and employing dissolve/erosion type feeders such as for example a flow through feeder.
The manual dumping process has numerous drawbacks including exposing personnel to potentially hazardous chemicals. Another drawback associated with the manual dumping process is the deterioration of activity of the biocide when the dry granular biocide is exposed to ambient humidity.
It is well known by those skilled in the art that dissolve/erosion type feeders are employed to introduce low solubility bromine biocides to aqueous systems. Generally, the dissolve/erosion feeder operates by establishing a flow of water through the feeder to cause surface friction between adjacent biocide granules or tablets thus eroding the surface thereof and dissolving the displaced particles. The dissolve/erosion type feeders have several drawbacks. Because the rate of dissolution of the biocide granule or tablet is dependent upon the water temperature and the rate of flow of the water, it is difficult to monitor the amount of biocide introduced to the aqueous system. At higher water flow rates, the rate of erosion exceeds the rate of dissolution of the displaced biocide particles, thus resulting in undissolved biocide entering the aqueous system. This latter limitation substantially prevents increasing the amount of biocide that may be added to the aqueous system in response to an isolated increase in microbial growth. Another drawback of dissolve/erosion type feeders is the safety concern of generating nitrogen trihalides, such as for example nitrogen trichloride or nitrogen tribromide, from the wet oxidant under normal conditions of operation or storage. It will be appreciated by those skilled in the art that employing dissolve/erosion type feeders make it difficult if not impossible to effectively make an addition of a discrete or selected amount of a biocide to maintain a desired concentration of the biocide. An example of a dissolve/erosion type feeder is the feeder identified as Model BF-10 commercially available from Calgon Corporation, Pittsburgh, Pa., U.S.A.
U.S. Pat. No. 3,626,972 (Lorenzen) discloses a soluble granule feeder for use in swimming pools having a pump joined to suction and return lines wherein each feeder is said to comprise a mixing tank open to the atmosphere and connected to a granule supply bin. This patent states that a bypass conduit taps the return line to supply liquid from a portion of the return line flow to the mixing tank. This patent states that a mixing tank open to the atmosphere receives chlorine granules that are mixed with a measured amount of water to create a chlorine solution that is then passed through a Venturi unit to the swimming pool system. In contrast, the process of the instant invention does not employ a mixing tank or a valving cylinder responsive to a float, and eliminates the problems associated with antimicrobial compositions exposure to the atmosphere and ambient humidity. Further, the process of the instant invention delivers the antimicrobial composition in dry granular form to the aqueous system being treated.
U.S. Pat. No. 3,710,817 (Lorenzen) discloses an apparatus for adding solute to a liquid such as swimming pool water in which a first mixing tank is supported on a second mixing tank, each of which is connected to the water circulating system of the pool. This patent states that the apparatus comprises a first mixing tank, a second mixing tank, means for bypassing a portion of the recirculating water into the bottom of the first mixing tank, means controlling the water level within the first mixing tank at which water is transmitted into the second mixing tank, and means for connecting the second mixing tank to suction means such as a circulation pump or a venturi in the pump line such that the second mixing tank has a float controlled valve which releases the water and solute to the suction side of the venturi or pump. This patent states that the means for controlling the water level within the first mixing tank effects the dissolution of the proper number of soluble chlorine cakes within the first mixing tank that are exposed to circulating water for the period that the pump is turned on. This patent states that the number of chlorine cakes exposed to the water at any one time determines the concentration of the chlorine delivered to the second tank.
In spite of this background material, there remains a very real and substantial need for a process for delivering PG,7 a selected effective amount of a dry granular antimicrobial composition to an aqueous system. More specifically there is a substantial need for a process for safely delivering, with substantially no human exposure, a selected effective amount of a dry granular antimicrobial composition to an aqueous system and a process wherein the amount of biocide remaining in inventory may be determined. Further, there is a very real and substantial need for a process of delivering a selected effective amount of a dry granular antimicrobial composition to an aqueous system wherein the delivery of the dry granular antimicrobial composition to the aqueous system is not affected by a specific amount of water, water flow rate or temperature. Additionally, there remains a need for a process for delivering a dry granular antimicrobial composition to an aqueous system wherein the effective quantity of the dry granular antimicrobial composition delivered may be varied over a broad effective range with a single operation.